Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1998-10-09
2002-04-09
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C313S502000, C313S504000, C313S506000
Reexamination Certificate
active
06368730
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electroluminescent device made of an organic light emitting material, which is used in a light emitting display, a light emitting diode and a surface light emitting source.
An electroluminescent device (EL) is a device utilizing a phenomenon of light emission when electric field is applied to a certain light emitting material. A display made of the electroluminescent device can realize a thin type display with wide angle of visual field and low dissipation power because it is capable of spontaneously emitting light and no back light is required. The display also has a feature that it can perform high-speed response. However, since the light emitting efficiency of a conventional light emitting material is low, luminance of the display was insufficient. There was also a problem that it was difficult to realize a color display because light emitting color of the light emitting material was limited.
Recently, an excellent electroluminescent device using an organic compounds as a constituent material has been reported (e.g. related paper, Applied Physics Letters, vol.51, 1987, p.913). In this report, C. W. Tang et al. disclose an injection type electroluminescent device having a structure that an organic light emitting layer and an electric charge transporting layer are laminated. In case of this electroluminescent device, an excellent electroluminescent device having high luminance is obtained by using a tris(8-quinolinol)aluminum complex (hereinafter abbreviated to Alq) having both high light emitting efficiency and high electron transporting ability as the light emitting material.
In Journal of Applied Physics, vol.65, 1989, p. 3610, it is reported that an organic light emitting layer is formed with Alq which doped with a fluorescent dye such as coumarin derivative, DCM
1
(Eastman Chemicals) or the like, and a light emitting device using that organic layer is made and a luminescent color of the device changes by proper selection of the dye. It is also disclosed that the light emitting efficiency is enhanced compared with a non-doped device.
Various researches and developments have been made subsequent to this study. As a result, a fluorescent metal chelete complex, an electron transporting organic molecule and a hole transporting organic molecule have been developed as a new light emitting material and a development of a light emitting material for color display having high luminance has rapidly been advanced.
Various electrode materials suited for these light emitting materials have also been studied. For example, Japanese Patent laid-Open Publications Nos. 60-165771 and 5-121172 disclose a metal thin film electrode made of metals having a small work function such as Mg—Ag, Ca, Ag, Li—Al, Li—Ag, Al and the like as an electron injection electrode, which is formed by deposition.
However, the above electroluminescent device has a problem that life is short. Since the light emitting material and electrode material are easily affected by water, these materials are considerably deteriorated by moisture absorption of the device. Electroluminescence essentially occurs by electronic conduction in the light emitting material, but in the presence of water, conduction of ions simultaneously occurs. When the light emitting efficiency is lowered by such phenomena, a driving voltage of the electroluminescent device is increased and luminance is lowered. As a result, a dark spot is formed at the portion where luminance is considerably lowered.
Various display panel structures for color display have also been studied, together with the development of the material As a structure of a color panel, a structure wherein light emitting layer patterns of three colors are arranged on one substrate is most popular. However, since this structure requires three patterning processes for forming light emitting layer patterns on one substrate, there can be caused problems such as deterioration of each light emitting material due to chemicals and water during the patterning processes, and low yield of the process. To avoid these problems, Japanese Patent Laid-Open Publication No. 7-114350 discloses a color panel structure that three monochromatic panels are superposed. In this publication, each monochromatic panel comprises a transparent made of an acrylic resin or glass substrate. However, a color display panel having this structure is very thick and has a problem that, since adjacent picture element electrodes are separated each other in back and forth, light shadow is formed by each of picture element electrodes and, therefore, resolution and color separation at the time of diagonally observing the picture plane are insufficient and thus high picture quality is not obtained. There is also a problem that the substrate is liable to be broken by distortion on lamination when the substrate is made of glass.
SUMMARY OF THE INVENTION
The present invention has been developed to overcome the above described disadvantages.
A first object of the present invention is to solve the above conventional problems by improving a transparent substrate and a transparent electrode, and to provide an injection type excellent electroluminescent device which hardly causes change in luminance with a lapse of time and has few dark spots.
A second object of the present invention is to provide an injection type electroluminescent device which hardly causes change in luminance with a lapse of time and has few dark spots, and which is thin and flexible, by using a new sheet material as a transparent substrate.
A third object of the present invention is to provide an excellent color electroluminescent display panel which hardly causes change in luminance with a lapse of time and has few dark spots, and is thin in thickness, superior in resolution and color separation and easily produced.
In accomplishing the first object, a first aspect of the present invention is an electroluminescent device comprising a transparent anode formed on a transparent substrate; a thin film cathode containing an alkali metal or an alkali earth metal; an electron transporting organic molecule and a hole transporting organic molecule between a pair of electrodes consisting of said transparent and said thin film cathode; and a barrier sheet for covering the outer surface of said thin film cathode; wherein both of the surface of said transparent substrate and the surface of said transparent anode have a hydrophobic surface with a molecular structure without having active hydrogen. With this construction, the water content of the device is reduced from the beginning and, at the same time, penetration of water is inhibited, thereby making it possible to obtain an excellent electroluminescent device which hardly causes change in luminance with a lapse of time and has few dark spots.
In accomplishing the second object, a second aspect of the present invention is an electroluminescent device comprising a transparent anode formed on a transparent substrate; a thin film cathode containing an alkali metal or an alkali earth metal; an electron transporting organic molecule and a hole transporting organic molecule between a pair of electrodes consisting of said transparent and said thin film cathode; and a barrier sheet for covering the outer surface of said thin film cathode; wherein said transparent substrate comprises:
(a) a two-layer polymer film comprising an adhesive hydrophobic polymer layer containing at least one functional group selected from the group consisting of amino group, amide group, hydroxyl group and carboxyl group in the concentration of not more than 1% by weight and a hydrogen-bonding polymer layer containing at least one functional group selected from the group consisting of amino group, amide group, hydroxyl group and carboxyl group, or
(b) a three-layer polymer film comprising said hydrogen-bonding polymer layer, a hydrophobic polymer layer made of at least one kind selected from the group consisting of polyolefin, polyvinylidene chloride, polyvinyl chloride, polyacrylonitrile, flu
Inaba Ritsuo
Kishimoto Yoshio
Garrett Dawn
Kelly Cynthia H.
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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